as it should be! i think that neither "all decryption is testimonial" or that "no decryptions are testimonial" are good policies. imho, decryptions should be treated in the same manner as other paper based evidence production requests: most of the time, the government cannot compel you to produce evidence testifying against you, but there are certain exceptions ("foregone conclusions" included).
> What if this was a murder case and the defendant had stored notes about his murder on the computer?
i don't think you're interpreting the "foregone conclusion" doctrine correctly. what it means is that keys, passwords, decryptions, etc cannot be used for the police to go on fishing expeditions for evidence. if they know you have incriminating evidence and can show that, then they can compel the production of that evidence. this is something that happened in US v Fricosu, in which Fricosu actually was compelled to decrypt. note that this ruling, which does not compel decryption, is entirely consistent with US v Fricosu
not if it knew that these documents were under your control and were incriminating. what exactly suggests your reading? the opinion was pretty specific about how the government could not prove the existence of any specific incriminating files on the defendant's drive, and thus, it was not a foregone conclusion
> the murder case ... possession of those files alone would not constitute a crime
whether the possession of the files is in and of itself a crime is irrelevant to the fifth amendment. the only thing that matters is whether your testimony can be used to incriminate yourself.
> Given the dicta in this case, however, it is arguable that, even in such a scenario, a defendant would be able to prevent decryption, thus creating an inconsistency with Fricosu
Author of the article disagrees. From the article:
> Also note that the court’s analysis isn’t inconsistent with Boucher and Fricosu, the two district court cases on 5th Amendment limits on decryption. In both of those prior cases, the district courts merely held on the facts of the case that the testimony was a foregone conclusion.
However, in addition to that, the court notes that there are two reasons why the Fifth Amendment prevents compelled description. Besides the foregone conclusion doctrine, there is discussion such at 22: "the decryption and production of the hard drives would require the use of the contents of Doe’s mind and could not be fairly characterized as a physical act that would be nontestimonial in nature. We conclude that the decryption and production would be tantamount to testimony by Doe of his knowledge of the existence and location of potentially incriminating files; of his possession, control, and access to the encrypted portions of the drives; and of his capability to decrypt the files." This to me implies the court's belief that the act of production would be testimonial because it would imply that Doe possesed and had access to incriminating files. Since possessing and having access to child pronography is a crime, that alone--that act of him affirming that he had access to such files by providing a decryption key--would incriminate him. By implication, this would not be the case if possession of certain docuemnts was not itself a crime, yet these documents could be incriminating.
The court spends 2 paragraphs discussing this, but I think it is not inconceivable that this sort of argument could be applied to other cases where the foregone conclusion doctrine might otherwise be succesfully applied to compel decryption, since ostensibly any 1 of the court's two points could be used to prevent compelled decryption. I wonder if this conclusion is based solely on the nature of the crime alleged here, or would be applicable to other crimes where merely showing that you have possession to access to incriminating documents is not itself a crime, as in child pornography.